It is you, but not in the sense that your learning ability is subpar. Almost certainly it is because your native tongue doesn't feature inflection endings the way German does, and apart from the problems of memorizing the values, you have to cope with the concept of them being there at all. This isn't something that you can sidestep - it comes to you after a ...

In addition to those exceptions mentioned before (nouns with -n and -s ending in plural) you shouldn't add an -n in dative in most nouns with non-native plural endings (not only English/French "s", but also Latin or Greek endings). E.g. den Tempora (plural of Tempus - "tense"), den Modi (plural of Modus - "mode"), den Praktika (plural of Praktikum - ...

Very probably it is not your difficulty but the fact that German grammars have not found yet a way of presenting the adjective declensions in a reasonable form.
There are tree types:
1 After sein the adjective has no ending: Der Mann ist alt.
2 There is an adj declension with the endings e/en.
If you look at such a declension table you see you don't have ...